Gypsum lath construction



y 968 G. w. GREEN 3,382,636

GYPSUM LATH CONSTRUCTION Filed July 24, 1964 IN VEN TOR.

ATTORNEYS United States Patent 3,382,636 GYPSUM LATH CONSTRUQTION GeorgeW. Green, West Chester, Pa, assignor, by mesne assignments, toGeorgia-Pacific Corporation, Portland, Greg, a corporation of GeorgiaFiled July 24, 1964, Ser. No. 384,893 3 Claims. (Cl. 523ltl) ABSTRACT OFTHE DISCLGSURE A paper covered gypsum lath construction having uniquewater absorbing characteristics is di closed for use with thin coatingplasters. The paper is coated with a wetting agent, such as an alkylaryl sulfonate, an alkyl ester sulfonate or an alkyl aryl ether, and thepaper is provided with pin holes distributed over the vsurface thereof.

This invention relates to improvements in gypsum lath and moreparticularly, to a paper covered gypsum lath construction while hasunique water absorbing characteristics.

While not limited thereto, the invention is especially suitable whenused as a base for the 'so-called thin coat plastering systems whichhave been developed recently. In accordance with the techniques whichare employed, a single thin finished coating ranging from to inthickness is applied directly to the lath to give a wall having the sameappearance as obtained with conventional multi-coating plasteringsystems.

In the use of these thin coat plasters, problems arise because the thincoating contains a large amount of water when applied. Until asignificant amount of this moisture is removed from the plaster, itcannot be properly troweled. Air-drying has been found to take .so muchtime that the plaster may be So close to the point of setting when it isin a trowelable condition that insuflicient time is left to do thetroweling job satisfactorily. For this reason, it has been the practiceto apply a relatively rough base coat which is porous and absorbent andthen to cover the base with the relatively thin finished coating. Thispractice is somewhat self-defeating since the material and labor savingswhich were expected to be gained with these thin coat plastering systemscannot be realized when more than one coat is applied.

Considerable effort has been made to eliminate the use of this basecoat. One recent approach that has been partially successful inovercoming the problem involves the use of a paper covering for thegypsum lath which is provided with tiny pin holes over the surface whichis to be covered with the thin coat of plaster. The pin holes providepassageways through the paper which permit the water in the plaster topass through to the relatively absorbent gypsum core. The use of thispin holed paper creates sufiicient suction to prevent sagging ofconventional thicker coats of plaster but still does not give a greatenough increase in troweling time to be satisfactory when thin coatplasters are applied. This is believed to be because the surface tensiontends to build up around and within the holes after an initial portionof the water in the plaster is absorbed, following which little or nowater may be absorbed.

Surprisingly enough, we have discovered that by coating the surface ofpin holed paper with a wetting agent, an extremely rapid withdrawal ofthe moisture in the thin coat of plaster is effected. The moisturewithdrawal rate is not only much faster than that achieved by usingeither the pin holed paper :alone or the wetting agent alone, but alsomuch greater than might be expected as a result of the combination. Infact, in typical samples it has been found that moisture withdrawaltakes place at a rate 3,382,635 Patented May 14, 1958 ice of about tentimes that achieved when using pin holed paper alone and about threetimes that which is achieved when using treated paper alone. Thus, theinvention provides an extremely effective and simple means of increasingthe troweling time available to the plasterer and also improves thefinished surface resulting when using the new thin coat plaster.

How the foregoing and other objects of the invention are achieved willbecome more fully apparent from the following description and theaccompanying drawings in which:

'FlGURE l is an isometric projection showing, in somewhat enlarged form,a piece of gypsum lath manufac tured according to the present invention;and

FIGURE 2 is an enlarged sectional view of a portion of a lath of thetype shown in FIGURE 1.

In accordance with the present invention the lath 1 comprises a gypsumcore 2 generally having a thickness of about The core 2 is sandwichedbetween sheets 3 of relatively smooth paper which may be coated on oneside with an adhesive in order to secure the product together. Thethickness of the paper is somewhat exaggerated in the drawings forpurposes of illustration and in practice is the same as thatconventionally used in the manufacture of lath of this type and may be,for example, in a typical product, about & thick. Typical lath piecesare 4 by 8 although other sizes may obviously be made if desired.

One side of the lath shown in the drawings is provided with smallapertures or pin holes 4. While both sheets of paper may be providedwith these pin holes, as a convenience to the plasterer in constructingwalls and partitions, only one sheet need be so treated in carrying outthe invention. These holes need be merely pin p-rioks having a diameterof about although larger holes as large as t," may be employed ifdesired. The holes should extend through the paper and through anyadhesive coating thereon.

As shown in the drawings, the holes are placed in relatively closelyspaced rows, the holes going generally spaced on about centers. Whilethe rows could be staggered if desired, the aligned arrangement shown inFIGURE 1 works very effectively.

As was mentioned above, the holes provide passageways for the excesswater to pass into the relatively absorbent gypsum. core. Upon carefulanalysis and study, however, I have determined that while the rate ofmoisture withdrawal is satisfactory for a short while after the plasteris applied with lath of this type, it very shortly tends to slow down.More often than not, there is not sufficient troweling time availablewhen a thin coat of plaster is applied to this type of lath. In carryingout the invent-ion, I have found that when pin holed paper is treatedwith a wetting agent the finished lath will continue to withdraw enoughmoisture from the thin coat of plaster so that within a relatively shorttime after application, the plaster has reached a workable consistency.While the reasons for this result are not fully understood, it isbelieved that the wetting agent carried by the plaster prevents thebuild-up of surface tension in the water which collects in and aroundthe holes shortly after the plaster is applied.

Various wetting agents which are capable of causing water to rewet andrepenetrate the paper at a substan tially faster rate than paper nottreated with the substance can be employed in accordance with theinvention. The several types which are commercially available are quitesatisfactory, and there do not appear to be any serious limitations onthe types which may be used,

ased on chemical considerations, aside from that of generalcompatibility with paper and gypsum plaster.

In particular, the sulfonated organic wetting agents give verysatisfactory results. One example is the alkyl aryl sulfonate sold underthe trade name Ultrawet 30- DS as made by the Atlantic Refining Company,Philadelphia, Pa. This is an anionic liquid material believed to be analkyl benzene sodium solfonate. Another sulfonated anionic wetting agentwhich gives good results is the alkyl ester sulfonate sold under thetrade name Nopco 2272-R as made by Nopco Chemical Company, Harrison,N.J., which is believed to be a sulfonated fatty butyl ester.

Still another effective wetting agent which has been employed is anon-ionic material sold under the trade name Triton X120 by the Rohm &Haas Company, Philadelphia. This is an alkyl aryl ether believed to bean alkyl aryl polyetlher alcohol.

The wetting agent can be applied to the paper at any stage of themanufacturing process, for example, on the surface of the paper at thecalendar stack at the paper mill or it may be applied to the finishedperforated lath. In accordance with the preferred practice, however,gypsum lath is manufactured by applying paper previously treated at thecalendar stack to the gypsum core and then the finished product isperforated with the pin holes. When following this practice, anon-volatile agent should be employed to avoid its volatilization in theboard mill kiln, which may subject the paper to temperatures of about200 F. For economic reasons the Wetting agent is preferably applied as adispersion on the surface of the paper.

In the following table the time required for three drops of Water to beabsorbed was measured and the results illustrate the effectiveness oflath treated with Nopco 2272-R in accordance with this invention:

Lath faced with: Time in seconds Untreated paper 250 Pin holed alone 73Treated paper alone 25 Treated and pin holed paper 7 In this test, sixdrops of water at 72 F. are delivered to the paper and the time measuredwithin which exactly three drops have disappeared.

Lath produced in accordance with this invention has proved to be veryeffective in practice in giving the plasterer sufiicient working time totrowel the product, since the plaster reaches a workable consistencymuch more quickly than has heretofore been the case. There is verylittle Waiting period before it can be troweled. Plastering systemsusing lath constructed according to the present invention contribute inlarge measure to the success of the thin coat plastering systems, makingpossible equal or superior results to those gained by conventionalplastering methods, with significant savings in cost.

I claim:

1. A gypsum plaster board product comprising; a relatively solid gypsumcore, paper facingv sheets overlying said core on each side thereof, atleast one of said sheets consisting of pin holed paper, the pin holes insaid paper being distributed over the entire surface thereof andextending therethrough to provide for the passage of water into thecore, the exposed surface of said perforated paper being coated with awetting agent.

2. A gypsum plaster board product comprising; a relatively solid gypsumcore, paper facing sheets overlying said core on each side thereof, atleast one of said sheets consisting of pin holed paper, the pin holes insaid paper being distributed substantially over the entire surfacethereof and extending therethrough to provide for the passage of waterinto the core, the exposed surface of said perforated paper being coatedwith a wetting agent selected from the class consisting of alkyl arylsulfonates, alkyl ester sulfonates, and alkyl aryl ethers.

3. A gypsum plaster board product comprising; a relatively solid gypsumcore, paper facing sheets overlying said core on each side thereof, atleast one of said sheets consisting of pin holed paper, the pin holes insaid paper being distributed substantially over the entire surfacethereof and extending therethrough to provide for the passage of waterinto the core, the exposed surface of said perforated paper being coatedwith a non-volatile organic wetting agent.

References Cited UNITED STATES PATENTS 907,877 12/1908 Rader 156-461,464,360 8/1923 Hicks 156-46 1,538,087 5/1925 Buttress 15644 2,342,4622/ 1944 Farmer et a1. 15644 2,408,488 10/ 1946 Sorensen 15646 2,711,3776/1955 Riddell 156-44 2,879,662 3/1959 Spinelli 161-113 ROBERT F.BURNETT, Primary Examiner.

ALEXANDER WYMAN, Examiner.

R. H. CRISS, Assistant Examiner.

